A wing simultaneously heaving and pitching can extract energy from an oncoming water or air stream. First large-scale commercial demonstrators are being installed and tested. The operating conditions of this device is likely to feature Reynolds numbers in excess of 500,000. Strong finite wing effects spoiling the power generation efficiency are also expected. This paper thoroughly investigates the hydrodynamics of oscillating wings at a Reynolds number of 1,500,000 considering finite wing effects for an aspect ratio 10 wing with either sharp tips or endplates to reduce tip vortex losses. The study of these periodic flows uses three-dimensional time-dependent Navier-Stokes simulations with grids featuring more than 30 million cells The shear stress turbulence model of Menter is used for the turbulence closure. Main contributions include: a) the quantification of the efficiency improvement achievable by using wings with endplates rather than bare tips, and b) detailed comparisons of the wing hydrodynamics with and without endplates, and the infinite wing,